This invention relates to lead-acid batteries and particularly to the provision of a leakage/corrosion barrier for insert molded terminals of the battery.
Sulfuric acid electrolyte readily wets the surfaces of internal lead components which are joined to the output terminals of a battery via lead connector parts insert molded within plastic partition walls (including the cover). This results in leakage at the output terminal(s) of the battery.
The foregoing leakage and corrosion problem is amplified when the battery is heat cycled, that is battery service occurs over widely varying ambient temperatures. Since the plastic materials forming the partition walls of the battery typically have a different coefficient of thermal expansion than the lead connector parts enshrouded by the plastic, there is a tendency for the plastic and lead connector parts to separate and create a void for the passage of acid electrolyte. Attempts to overcome this problem have included the provision of collars or ribs on the connector to increase the length of the interfacial path between the lead connector and enshrouding plastic, as well as the provision of an interposed layer of thermosetting resin (see U.S. Pat. No. 4,758,482 to Yamana et al.), or two layers of thermoplastic rubber and plastic materials of differing elasticities (see U.S. Pat. No. 4,522,899 to Illmann et al.). Electrolyte creepage between internal terminals of a battery in a through-the-partition connection has been suppressed by coating the intercell lead connector with a perfluoro surfactant prior to application of a surrounding plastic filler (see Japanese Patent Publication No. 58-25079 published Feb. 15, 1983).
In non-insert molded terminal constructions it has been common to use rubber O-rings or rubber undercoat layers applied to a lead post member extending through an aperture in a preformed plastic partition wall, and the use of a secondary epoxy seal, to limit electrolyte creepage (see U.S. Pat. No. 4,683,647 to Brecht et al.).